Hybrid hard disks may integrate non-volatile memory device such as flash memories into the hybrid hard disks to support read or write caching and burst read mode. However, in redundant arrays of independent disks (RAID) environment, integrated non-volatile memory devices may be bundled into individual hybrid hard disk and they may not be utilized by RAID in a more effective way. For example, a first non-volatile memory device in a first hybrid hard disk is isolated from a second non-volatile memory device in second hybrid hard disk and can not be shared by the second hybrid hard disk. A non-volatile memory device may store logical data that may be image of raw data on the hybrid hard disk. Redundancy brought by a RAID system may cause unnecessary redundancy of non-volatile memory devices inside hybrid hard disks. For example, in a RAID 1 or 0+1 implementation, one or more non-volatile memory devices may be wasted. For other multiple hard disk systems, in normal situation, a majority of system loading at a time may be on one hard disk only. In such a situation, non-volatile memory devices on an idle disk may be wasted as well.